Emulsifiers can be largely classified into low molecular emulsifiers and high molecular emulsifiers. The low molecular emulsifiers are the so-called surfactants, and include fatty acid soaps, glycerin esters and sugar esters. High molecular emulsifiers include natural substances such as gum arabic and other rubbers and casein, as well as synthetic products such as acrylic acid salts and polyvinyl alcohols.
These emulsifiers are used in appropriate admixture depending on the purpose of use, but low molecular emulsifiers generally have the disadvantage of susceptibility to pH changes and loss of an emulsifying property as a result of changes in concentration resulting from salt addition or dilution.
Because the natural high molecular substance gum arabic must be used at a high concentration to achieve stable emulsions, while its supply volume is highly dependent on the weather conditions in the producing nation and its cost is highly variable, there has been a need in recent years for natural high molecular emulsifiers which can be provided in stable supply. On the other hand, synthetic products such as polyacrylic acid salts and polyvinyl alcohols are often limited in their uses because of problems with their emulsifying properties. An additional problem of natural high molecular emulsifiers is that they generally have high viscosity even at low concentrations, and thus their handleability is poor during the preparation of emulsions.
As mentioned above, emulsifiers employed for a variety of uses must provide emulsions which maintain a stable emulsified state over long periods, and when used in foods they must provide an appropriate taste and texture.
For example, although gum arabic is widely used as an emulsifier for emulsified aromatics, it has the problems mentioned earlier. Also, xanthan gum is widely used as an emulsifier for mayonnaise and dressings, but it gives highly viscous products and does not always provide the desired texture. In addition, casein used in creams such as coffee cream is not always satisfactory because of its high susceptibility to pH changes and the breakdown of its emulsions upon dilution.